1. Technical Field of the Invention
This invention relates to electrical conductors with joint grounding means and, more particularly, to electrical multiple conductor cables having a built-in cable shield bonding system.
2. Description of the Prior Art
When a cable sheath opening is made for the purpose of installing a cable terminal or closure, the electrically conductive shield is cut away. To provide shield continuity in a cable system, each closure and cable terminal must have provision for through bonding the cable shield. The electrical conductivity of this bond should be equivalent to that of the cable shield.
Bonding hardware which is used to restore the shield continuity generally consists of a pair of clamps which are attached to the shield at each end of the opening. These clamps are electrically connected to each other by a metal bar or wire.
One example of the type of clamp that is employed for this purpose is disclosed in U.S. Pat. No. 3,757,269, issued in the name of R. G. Baumgartner et al on Sept. 4, 1973. (This patent was subsequently reissued and bears U.S. Pat. No. Re. 28,468.) The Baumgartner et al patents relate to a cable shield connector for providing electrical shield continuity at splice points or terminals. This connector utilizes contoured plates between which the shield and plastic outer jacket of the cable section are clamped. The inner plate has an upstanding tang or tab on one end and an upwardly protruding threaded stud spaced from the tab. The other end of the inner plate is slipped beneath the shield and an outer plate is mounted on the stud over the exterior of the plastic jacket. As the plates are forced toward each other, the outter plate first contacts the tab and tends to pivot thereabout tightly clamping the shield and jacket between the ends of the plates. The inner plate can have an insulating layer on its underside to prevent shorting of the cable conductors to the cable shield if damage occurs to the conductor insulation.
An illustration of the use of this type of shield connector appears in U.S. Pat. No. 3,971,894, issued in the name of C. W. Faust et al on July 27, 1976. Faust et al disclose apparatus for enclosing splices between two or more multiconductor cables. This apparatus includes a unitary support member which has affixed thereto cable ground shield bonding circuitry.
While the above-described Baumgartner et al shield connector, when used in the manner set forth in Faust et al, provides good ground shield continuity at the point of entry into the cable, it should be noted that the installation of the bonding hardware is a field operation. Consequently, the quality of the shield bond is craft dependent. In some cases the bonding job is either done incorrectly or not at all. This failure to effect a proper shield bond can lead to degradation in transmission performance.
An indication of the state of the art in cable design can be obtained from a review of U.S. Pat. No. 4,002,819 issued in the name of L. V. Woytiuk on Jan. 11, 1977 and U.S. Pat. No. 4,004,077 also issued in the name of L. V. Woytiuk on Jan. 18, 1977. The Woytiuk '819 patent discloses an electric cable having a multistranded core of insulated conductors and a jacket. A mixture which forms a blockage to the penetration of water at least partially fills the spaces between and around the conductors. Surrounding the conductors and the water blockage mixture is a core wrap. Between the core wrap and a metal sheath is a filler of water repellant calcium carbonate and high molecular weight resin mix. The jacket forms the outer layer of the cable adjacent the metal sheath.
The Woytiuk '077 patent discloses a very similar cable to that described above. The major differences are the compositions of the water blockage mixture and the filler between the core wrap and metal sheath.
It should be apparent that none of the aforementioned references deals with the problem of providing an electrically conductive ground shield which is capable of remaining intact along a portion of its periphery when the insulative cable sheath or jacket and the metal sheath or shield are entered to gain access to the inner conductors.